The diagnostic value of amniotic fluid Gram stain examination and limulus amebocyte lysate assay in patients with preterm birth.

The purpose of this study was to determine the value of Gram stain examination and Limulus amebocyte lysate (LAL) test in the detection of intraamniotic infection. Ninety women with preterm labor and intact membranes (n = 55) or preterm premature rupture of membranes (PROM) (n = 35) who delivered prematurely were included in the study. Amniotic fluid was cultured for aerobic and anaerobic bacteria as well as for mycoplasmas. Amniotic fluid analysis included Gram stain examination and limulus amebocyte lysate tests. The prevalence of positive amniotic culture was 32.2% (29/90) and the most common isolate was Ureaplasma urealyticum. Patients with preterm PROM group had a higher rate of infection than those with preterm labor and intact membranes 57.1% (20/35) vs. 16.4% (9/55), respectively (p = 0.0001). We found a lower gestational age at delivery and lower mean birth weight in neonates born to mothers with a positive amniotic fluid culture than those with negative amniotic fluid culture. The combined use of Gram stain examination and LAL test had a sensitivity and specificity of 51.7% (15/29) and 95.1% (58/61) respectively for the detection of positive amniotic fluid culture. We conclude that Gram stain examination and LAL test are rapid, simple and specific tests that can be used to detect microbial invasion of the amniotic cavity except in patients with mycoplasmas infections.